Studies of an Atmospheric Fluidized Bed Combustor Using Cotton Stalk

Abstract

In the present work, combustion characteristics of cotton stalk based 7.5 MW atmospheric fluidized bed combustor at Malwa power plant limited (MPPL), Muktsar Sahib, Punjab, India have been studied. Operational data and various fuel samples have been collected from the plant site. A solid population balance model for fuel with wide size particle distribution (cotton stalk with particle size ranging between 0.75 mm to 80 mm) has been developed and optimized. Bed carbon load and carbon utilization efficiency are found to be rising with increase in fuel particle size modulus and distribution modulus. The solid population balance model has been optimized for maximum carbon utilization efficiency and minimum elutriation rate using multi-response optimization method. Fuel particle diameter, fuel feed rate and fractional excess air have been selected as input parameters and their optimal values are found to be 15 mm, 1.5 kg/s and 0.3 respectively. A three-phase exit gas composition model (considering bubble growth along bed height) has been developed. Model can predict exit gas composition from the fluidized bed combustor (FBC) using cotton stalk. It has been found that oxygen conversion decreases with rise in fractional excess air supply. First law of thermodynamics (energy) and second law of thermodynamics (exergy) based thermodynamic model has been developed and optimized in the present work. It has been found that the boiler is the source of maximum exergy destruction. The thermodynamic model has been optimized for overall plant exergy efficiency and complete cycle exergy destruction using multi-response optimization method. Turbine inlet steam pressure, turbine inlet steam temperature and fuel feed rate have been selected as input parameters and their optimal values are found to be 65 bar, 470˚C and 1.5 kg/s respectively. A brake-even analysis based economic study for maximum profit from the plant has also been conducted. In addition, agglomeration behavior of the cotton stalk under fluidized bed conditions has been studied experimentally.